The present invention relates to stents. More particularly, the present invention relates to stents having a web structure configured to expand from a contracted delivery configuration to an expanded deployed configuration.
Various stent designs are known in the art. These stents form vascular prostheses fabricated from biocompatible materials. Stents are typically used to expand and maintain patency of hollow vessels, such as blood vessels or other body orifices. To this end, the stent is often placed into a hollow vessel of a patient""s body in a contracted delivery configuration and is subsequently expanded by suitable means, such as by a balloon catheter, to a deployed configuration.
A stent often comprises a stent body that is expandable from the contracted to the deployed configuration. A common drawback of such a stent is that the stent decreases in length, or foreshortens, along its longitudinal axis as it expands. Such shortening is undesirable because, in the deployed configuration, the stent may not span the entire area inside a vessel or orifice that requires expansion and/or support.
It therefore would be desirable to provide a stent that experiences reduced foreshortening during deployment.
It also would be desirable to provide a stent that is flexible, even in the contracted delivery configuration.
It would be desirable to provide a stent having radial stiffness in the expanded deployed configuration sufficient to maintain vessel patency in a stenosed vessel.
In view of the foregoing, it is an object of the present invention to provide a stent that experiences reduced foreshortening during deployment.
It is another object to provide a stent that is flexible, even in the contracted delivery configuration.
It is also an object to provide a stent having radial stiffness in the expanded deployed configuration sufficient to maintain vessel patency in a stenosed vessel.
These and other objects of the present invention are accomplished by providing a stent having a tubular body whose wall has a web structure configured to expand from a contracted delivery configuration to an expanded deployed configuration. The web structure comprises a plurality of neighboring web patterns having adjoining webs. Each web has three sections: a central section arranged substantially parallel to the longitudinal axis in the contracted delivery configuration, and two lateral sections coupled to the ends of the central section. The angles between the lateral sections and the central section increase during expansion, thereby reducing or substantially eliminating length decrease of the stent due to expansion, while increasing a radial stiffness of the stent.
Preferably, each of the three sections of each web is substantially straight, the lateral sections preferably define obtuse angles with the central section, and the three sections are arranged relative to one another to form a concave or convex structure. When contracted to its delivery configuration, the webs resemble stacked or nested bowls or plates. This configuration provides a compact delivery profile, as the webs are packed against one another to form web patterns resembling rows of stacked plates.
Neighboring web patterns are preferably connected to one another by connection elements preferably formed as straight sections. In a preferred embodiment, the connection elements extend between adjacent web patterns from the points of interconnection between neighboring webs within a given web pattern.
The orientation of connection elements between a pair of neighboring web patterns preferably is the same for all connection elements disposed between the pair. However, the orientation of connection elements alternates between neighboring pairs of neighboring web patterns. Thus, a stent illustratively flattened and viewed as a plane provides an alternating orientation of connection elements between the neighboring pairs: first upwards, then downwards, then upwards, etc.
As will be apparent to one of skill in the art, positioning, distribution density, and thickness of connection elements and adjoining webs may be varied to provide stents exhibiting characteristics tailored to specific applications. Applications may include, for example, use in the coronary or peripheral (e.g. renal) arteries. Positioning, density, and thickness may even vary along the length of an individual stent in order to vary flexibility and radial stiffness characteristics along the length of the stent.
Stents of the present invention preferably are flexible in the delivery configuration. Such flexibility beneficially increases a clinician""s ability to guide the stent to a target site within a patient""s vessel. Furthermore, stents of the present invention preferably exhibit high radial stiffness in the deployed configuration. Implanted stents therefore are capable of withstanding compressive forces applied by a vessel wall and maintain vessel patency. The web structure described hereinabove provides the desired combination of flexibility in the delivery configuration and radial stiffness in the deployed configuration. The combination further may be achieved, for example, by providing a stent having increased wall thickness in a first portion of the stent and decreased wall thickness with fewer connection elements in an adjacent portion or portions of the stent.
Depending on the material of fabrication, a stent of the present invention may be either self-expanding or expandable by other suitable means, for example, using a balloon catheter. Self-expanding embodiments preferably are fabricated from a superelastic material, such as a nickel-titanium alloy. Regardless of the expansion mechanism used, the beneficial aspects of the present invention are maintained: reduced shortening upon expansion, high radial stiffness, and a high degree of flexibility.
Methods of using stents in accordance with the present invention are also provided.